1. Field of the Invention
The present invention relates to reading data from tape.
2. Background Art
Data storage systems including tape moving relative to a tape head are commonly used to store information due to the reliability, low cost, efficiency, and ease of use of such tape systems. Information may be stored on tape through a variety of means such as magnetic, optical, and the like. Tape may be made more useful and cost-effective by increasing the volume density of stored information. This may be accomplished by including more data tracks across a given width of the tape. While allowing more data to be stored, the increase in density of data tracks requires a narrowing of the width of the data tracks, a narrowing of the spacing between data tracks, or both. As data tracks are more closely spaced, positioning of the tape with respect to a tape head becomes more critical to reduce the possibility of errors introduced while reading or writing information.
Density of stored information may also be increased by reducing the thickness of the tape. Reducing tape thickness, however, also increases the likelihood of tape distortion. Various factors including tension, temperature, humidity, time, and the like may cause the width of tape to shrink or expand, creating transverse distortion. Such shrinkage or creepage affects the spacing between data tracks.
Tape may also be made more useful and cost-effective by increasing the rate of data storage and retrieval. Typically, high data rate access is achieved by reading or writing multiple tracks simultaneously. This is accomplished with a tape head having multiple read and write elements spaced across the width of the tape. Thus, as the tape moves past the head, multiple tracks may be written or read simultaneously. However, since the head geometry is relatively fixed, shrinkage or creepage which changes the spacing between data tracks may result in an increase in read errors or, if extreme, the complete inability to simultaneously read multiple tracks.
What is needed is to reliably read data recorded on tape that has experienced transverse distortion such as shrinkage, creepage, and the like. This ability is particularly useful when data recorded in one format is read by a next generation tape system having smaller read elements.
The present invention permits reading magnetic tape having transverse distortion by selecting between longitudinally offset read elements to read the data track. The read elements are part of a tape head having an azimuth angle relative to the tape which creates a transverse offset between the data read elements. Thus, a particular read element is selected to minimize the effects of any transverse tape distortion.
A method for reading data recorded on a tape having transverse distortion is provided. The data is written on a data track. The data is read by a tape head having an azimuth angle relative to the tape. The azimuth angle creates a transverse offset between a data read element on a first module and a corresponding data read element on a second module. A measure of the transverse distortion is determined based on reading a plurality of servo tracks recorded on the tape. Either the first module read element or the second module read element is selected for reading the data track based on the determined transverse distortion.
In an embodiment of the present invention, determining a measure of the azimuth angle includes reading a servo track recorded on the tape with a first servo read element located on the first module. The servo track is also read with a second servo read element located on the second module. The measure of azimuth angle is determined based on signals produced by reading with the first and second servo read elements.
In another embodiment of the present invention, determining a measure of the transverse distortion includes reading a first servo track recorded on the tape with a first servo read element located on a module. A second servo track recorded on the tape is read with a second servo read element located on the same module. The measure of transverse distortion is determined based on signals produced by reading with the first servo read element and the second servo read element.
In still another embodiment of the present invention, determining a measure of the azimuth angle includes reading at least one servo track recorded on the tape with each of a plurality of pairs of servo read elements. The measure of the azimuth angle is determined based on averaging azimuth angles determined from each pair of servo read elements.
In yet another embodiment of the present invention, the azimuth angle is determined based on reading at least one servo track recorded on the tape. Selecting either the first module read element or the second module read element for reading the data track is based on the determined azimuth angle.
In a further embodiment of the present invention, the measure of transverse distortion for a length of tape is determined before data is read from the length of tape.
In a still further embodiment of the present invention, regions exhibiting poor data read signal quality are precharacterized. Such regions might be inferred by a low signal-to-noise ratio (SNR) or by the incidence of error correction code (ECC) array transient errors such as full error correction code uncorrectable errors.
In a still further embodiment of the present invention, the azimuth angle is adjusted to change the transverse offset between the first module read element and the second module read element.
A system for reading information recorded on tape having at least one servo track and at least one data track is also provided. The system includes a tape head having at least a first module and a second module. Each module has at least one read element for reading data written on the tape. The tape head has an azimuth angle relative to the tape, the azimuth angle creating a transverse offset between each read element on the first module and a corresponding read element on the second module. A plurality of servo read elements are also included. Each servo read element is located on one of the modules. Each servo read element generates a servo read signal based on reading a servo track recorded on the tape. Control logic determines tape position error based on the servo read signals. The control logic determines whether to read the data track with the first module read element or the second module corresponding read element based on the determined tape position error.
A method for reading data recorded as a plurality of data tracks on magnetic tape is also provided. The data is read by a tape head having at least a first module and a second module. The first module has a plurality of read elements. The second module has a plurality of corresponding read elements. The tape head forms an azimuth angle with the tape. The azimuth angle creates a transverse offset between a data read element on the first module and a corresponding data read element on the second module. Each data read element on the first module is grouped into a first group and a second group. Each data read element on the second module is grouped into the first group if the data read element corresponds with a first module first group data read element. Each data read element on the second module is grouped into the second group if the data read element corresponds with a first module second group data read element. A measure of transverse distortion on the tape is determined. At least one data track is read with a first module first group data read element. At least one additional data track is read. The additional data track is read with either a data read element from the first module second group or a data read element from the second module second group based on the determined measure of transverse distortion.
The above objects and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.